This invention relates to a hand-held nebulizer system for delivering aerosolized medication to a patient, and more particularly to a passive inspiratory nebulizer system which delivers aerosolized medication only during the inspiratory phase of the patient's respiratory cycle.
Nebulization utilizes the venturi principle to fracture liquid medications into a fine aerosol mist, which a patient inhales, thereby absorbing the active ingredients of the aerosol across the pulmonary membranes to effect the desired treatment. It is a standard strategy for the therapeutic application of medicinal aerosols for a wide range of pulmonary dysfunctions, including asthma, COPD, bronchitis, cystic fibrosis, croup, etc.
One therapy employed in the respiratory care field for many years is Intermittent Positive Pressure Breathing (IPPB). This approach utilizes a machine which delivers medicated aerosols upon a patient's inspiratory effort, entrained in a stream of pressurized gas. Included in the machine is a highly sensitive control device which senses inhalation by the patient, and the resulting negative air pressure (as referenced from the ambient atmospheric pressure), causing the machine to apply a positive pressure flow of air through a T-connection or the like to a mouthpiece to assist the patient during such inhalation phase of each breathing cycle. However, to stop the stream of pressurized gas, the patient must firmly enclose the mouthpiece with his lips and positively seal the system to avoid any leakage, thus allowing pressure to build in the system, shutting it off.
Many older patients are too tired or confused to be able to cooperate in this effort, and a mask has to be fitted and firmly held over their mouth and nose, covering them. Even when sick, tired, and confused, many patients struggle. Obviously, this is not popular with either patients or practitioners.
In contrast to the IPPB approach, state of the art hand-held nebulizers, powered by pressurized gas from an outlet on the wall behind a patient's bed, or by an oilless compressor, run continuously during the entire twelve to fifteen minutes necessary to complete the medicinal nebulization prescribed for treatment of the disorder suffered by the patient.
In good health, the ratio of the time necessary for inhalation to exhalation is 1:2. That is, if it takes one second to inhale, it takes two to exhale. The essence of the dysfunction of most types of lung disease is the destruction of the structural integrity of the small airways of the lung, leading to their collapse on exhalation, and prolonging the expiratory phase of the cycle. This dysfunctional ratio may be as much as 1:4 or 1:5. Since deposition of the fresh medicinal aerosol onto the pulmonary membranes can occur only during the inspiratory phase of the respiratory cycle, nebulization during the expiratory phase is wasted, being blown into the room. While this result is obviously wasteful in terms of cost, it also makes it very difficult to ascertain how much medication is actually being received by the patient, because an unknown amount is being blown to the atmosphere during exhalation, so that the patient is unlikely to receive the exact dose prescribed by the physician.
Another alternative therapy which attempts to solve this problem is discussed in the inventor's prior U.S. Pat. No. 4,396,015. A prior art IPPB machine is employed with a modified T-connection airway device which is open to atmosphere at one end, thereby permitting the patient to inhale from and exhale to atmosphere rather than in a pressurized environment. To accomplish this, the pressurized breathing tube utilized in the IPPB system is removed, but a sensor tube between the machine and the airway device remains, so that the machine can sense the negative pressure signalling the inhalation cycle and provide pressurized gas to the nebulizer, and conversely shut off that pressurized gas when positive pressure is sensed, signalling expiration. To accomplish the desired function, the sensor tube is smaller than the diameter of the expired gas outlet port in the T-connection, so that the airway device remains open to the atmosphere.
The approach taught in the '015 patent is a vast improvement over previous prior art modalities, permitting the treatment time to be greatly shortened, and the aerosolized medication to be more accurately delivered. However, a customized T-connection airway device is required, having specific unique guide tube structure to accommodate the sensor tube. Since standardized T-connection airway devices are widely available in the industry, it is a significant disadvantage to require a customized version, both in terms of cost and availability. It is desirable, particularly in a hospital setting, to be able to stock only standardized airway devices, which are widely used, rather than to have to stock specific devices configured for only one application.
Another problem with the '015 patent approach is that the prior art IPPB machines are not sufficiently sensitive to the relatively small pressure changes generated by a sick and weak patient's respiratory cycle to reliably shut off the pressurized gas flow during the expiration cycle and to ensure that it is restored at the onset of inspiration. Accordingly, what is needed is a new driver for the passive inspiratory nebulizer system which is sensitive to extremely small pressure changes, is compact and lightweight for maximum portability, and is comprised of reliable and durable components.